Polycystic ovary syndrome (PCOS) affects 6-8% of women and is marked by excess testosterone (T), irregular menses, and sub- or infertility. The cause of PCOS is unclear, but persistently rapid gonadotropin- releasing hormone (GnRH) pulses contribute to high luteinizing hormone (LH) and diminished follicle- stimulating hormone (FSH) secretion, which in turn contribute to androgen excess and irregular ovulation. This defect is in part related to excess T, which interferes with the ability of progesterone (P) to suppress GnRH pulses. Similar abnormalities of GnRH pulses are observed in adolescent girls with hyperandrogenemia (HA), a condition that can lead to adult PCOS. Resistance to feedback by low P levels likely contributes to abnormal GnRH pulses in these girls, but how this could affect the normal pubertal sequence of GnRH secretion (or how it could contribute to development of PCOS) is unknown. Our long-term goal is to delineate mechanisms governing abnormal GnRH pulses in hyperandrogenemic pubertal girls who go on to develop PCOS. Nocturnal GnRH frequency does not change significantly from early to late puberty, whereas daytime frequency demonstrates a marked increase. Early data suggests that P acutely suppresses daytime, but not nighttime, GnRH frequency. This proposal involves the novel hypothesis that sleep-associated GnRH frequency and waking GnRH frequency are differentially regulated. Thus, during normal puberty, rising T levels reduce the ability of pubertal P levels to suppress waking GnRH pulses, accounting for the normal pubertal increase of daytime GnRH frequency. However, sleep-associated GnRH frequency remains constant since it is not influenced by pubertal levels of P. Early data imply that sleep-associated changes of GnRH frequency are diminished or absent in early pubertal HA. Thus, as soon as GnRH activity increases in girls with HA, waking GnRH frequency is elevated due to HA-induced resistance to P feedback (i.e., GnRH frequency is high over 24 hours). This promotes progression toward PCOS by increasing LH and reducing FSH levels. Overnight slowing of GnRH pulses normally persists into adulthood, being most prominent in the early follicular phase (when it is important to support FSH secretion and follicular development);but HA in PCOS interferes with such slowing. Aim 1 is designed to determine if wake and sleep LH (GnRH) pulse frequencies are differentially affected by P feedback. Studies will determine if P suppresses waking LH frequency to a greater extent (or more rapidly) than sleep-associated LH frequency, and if such an effect is diminished in girls with HA. Aim 2 is designed to formally evaluate the presence and cause of altered sleep-wake differences in HA. Aim 3 will investigate the importance of diurnal GnRH frequency changes by testing the hypothesis that maintaining a rapid overnight LH (GnRH) frequency in normal early follicular women results in reduced FSH. These experiments will provide key insights into mechanisms governing normal diurnal changes of GnRH secretion as well as the genesis of GnRH abnormalities in PCOS. This may lead to therapeutic targets for early PCOS. PUBLIC HEALTH RELEVANCE: Hyperandrogenemia during adolescence can represent a forerunner of adult polycystic ovary syndrome (PCOS), which affects 6-8% of women and is marked by excess testosterone, irregular menses, and infertility. The causes of PCOS are unclear, but abnormal pulsatile secretion of gonadotropin-releasing hormone (GnRH) plays a role in adults with PCOS and adolescent girls with excess testosterone. The data gathered through the proposed research will enhance understanding of the mechanisms controlling the normal developmental sequence of GnRH pulse secretion across puberty, and how this sequence is perturbed in the setting of excess testosterone all with a view to designing rational treatment strategies for the early stages of PCOS.